1. Field of the Invention
The present invention relates to a masterbatch composition used for thermoplastic resin modification which has low tackiness and good workability and a method for preparing the masterbatch composition.
More particularly, it relates to a masterbatch composition comprising polybutene and an ethylene.multidot..alpha.-olefin copolymer obtained by copolymerizing ethylene with an .alpha.-olefin and having specific characteristics, and to the method for preparing the masterbatch composition.
2. Description of the Prior Art
A variety of molded articles, sheets and films are prepared from thermoplastic resin by molding processes such as injection molding, extrusion molding, blow molding and inflation molding. The thermoplastic resin is generally blended with various kinds of liquid, solid or powdery modifiers, for example, plasticizers, fillers, dyestuffs, pigments, lubricants, antioxidants and other miscellaneous agents in order to provide the resin having characteristics required for each application. These modifiers are blended with the thermoplastic resin in advance, pelletized and used. Alternatively, masterbatch pellets having a higher content of the modifiers are previously prepared and used for molding after dry blending with the base resin. In particular, in case the modifiers are liquid, masterbatch pellets are widely prepared in advance and used after dry blending with the thermoplastic resin.
In case polybutenes are used for the above modifiers, masterbatch pellets having a higher polybutene content must be prepared. Polybutenes, however, cause the problems described below, because they are poorly compatible with other polyolefin resins: tackiness of the pellets increases either immediately after preparation or several days thereafter, due to bleeding of polybutene on the surface of the pellets; blocking of the pellets takes place with one another or bridging occurs in a hopper during the dry blending operation. As a result, the prescribed amount of polybutene cannot be blended or non-uniformity of the blended mixture results even though blending can be carried out. Thus, blending operations are very difficult.